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iridology

I
believed that the human body was some sort of remarkable
collection of intelligent organs and systems that worked
together almost magically to create a healthy unit. --Confessions
of a Former Iridologist

Iridology is the study of the iris
to diagnose disease. It is not part of the curriculum of any medical school
and its practitioners are not usually medical doctors. (Naturopaths
are not medical doctors.) According to
Wikipedia, iridology is not regulated or licensed by any governmental
agency in either Canada or the United States.

Iridology is based on the questionable assumption that
every organ in the human body has a corresponding location within the iris
and that one can determine whether an organ is healthy or diseased by
examining the iris rather than the organ itself.

Medical doctors see the
iris as the
colored part of the
eye that regulates the amount of light entering by a contractile opening in
the center, the pupil.
The lens brings the light rays to a focus, forming an image on the retina where the light
falls on the rods and cones, causing them to stimulate the optic nerve and transmit
visual impressions to the brain. Medical doctors and optometrists recognize that certain
symptoms of nonocular disease can be detected by examining the eye. If a
problem is suspected, these doctors then refer the patient to an
appropriate specialist for further examination. However, recognizing symptoms of disease by looking
in the eyes isnot what iridology is about. In fact, when
iridologists have been tested to see if they could distinguish healthy from
sick people by looking at slides of their eyes, they have failed. In a study
published in the Journal of the American Medical Association (1979,
vol. 242, 1385-1387), three iridologists incorrectly identified nearly all
of the study slides of the irises of 143 healthy and diseased people. “In
fact, they often read the irises of the sickest people as being healthy and
vice versa. They did not even agree with each other.” Similar results
involving five Dutch iridologists were published in the British Medical
Journal (1988, vol. 297, 1578-1581) (Lisa
Niebergall, M.D.).

Iridology goes way
beyond the claim that the eyes often provide signs of disease.
Iridologists maintain that each organ has a counterpart in the eye and
that you can determine the state of the organ's health by looking at a
particular section of the eye. The markings and patterns in the iris are
compared to an iris chart, which maps zones of the iris and links them to
parts of the body. No scientific investigation led to these charts;
instead, they are the work of intuition.

Ignatz von Péczely, a 19th-century Hungarian physician
is usually credited with inventing iridology. He got the idea for this novel diagnostic tool when he saw a dark streak in the eyes of a man he was treating for a broken leg and it
reminded him of a similar dark streak in the eyes of an owl whose leg he had broken years earlier. Von Péczely then went on to document similarities in eye markings and
illnesses in his patients. (According to
Wikipedia, von
Péczely's nephew, August von Péczely, dismissed the story about the dark
streaks as apocryphal. The Wikipedia article also notes: "Iridology is not
supported by any published studies and is considered pseudoscience by most
medical practitioners and eye care professionals." Even if the story is
apocryphal, I like it because it illustrates the
magical thinking of practitioners and
patients.) Others completed the map of the eye. A typical map
divides the eye into sections, using the image of a clock face as a base. So, for
example, if you want to know the condition of a patient's thyroid gland, you need not
touch the patient to feel for any enlargement of the gland. Nor do you need to do any
tests of the gland itself. All you need to do is look in the
iris of the right eye at about 2:30 and the iris of
the left eye at about 9:30. Discolorations, flecks, streaks, etc. in those parts
of the eyes are all you need concern yourself with, if it is the condition of the thyroid
you wish to know. For problems with the vagina or penis, look at 5 o'clock in the right
eye. And so on. An iridologist can do an examination with nothing more than an iridology
map, a magnifying glass, a flashlight, and a vivid imagination.

If von Péczely's reasoning is typical, we can surmise that he and other iridologists
deceived themselves by looking for and finding correlations between eye markings and
illness (confirmation bias). They were working with vague notions of "markings" and
"illness." Diseases may not have been precisely or accurately diagnosed in
many cases. They were able to validate iridology by finding many correlations that in fact
were not established as causal relationships by rigorously defined
controlled studies.
Some of their correlations may be accurate, but many are undoubtedly bogus, due to very
broad interpretations of "markings" and "disease." They found patterns
where in fact there are no patterns (apophenia). They misinterpreted data and gave extraordinary
significance to confirmations, while ignoring or not seeking disconfirmations. Many of
their confirmations may have been matters of
subjective validation.
We do not know how much the power of suggestion played in their patients'
illnesses. Many diagnoses were probably wrong, but no objective tests were done to check
out the validity of the diagnoses. Some diagnoses may have been correct but the
iridologists may have been using other signs besides eye markings to make their diagnoses.
Finally, much of the success of iridology is due to the same factors that
account for the success of acupuncture, homeopathy, and other forms of
so-called "alternative" medicine: placebo effects.

What is most peculiar about the iris is that each is unique and
unchangeable, so much so that many claim that the iris is a better
identifier of an individual than fingerprints.